1. Field of the Invention
The present invention relates to ink jet printers and, more particularly, to priming stations for priming and cleaning nozzles of an ink jet printhead.
2. Description of Related Art
Ink jet printers usually include one or more extended arrays of nozzles contained on a planar surface of a printhead. Droplets of ink are ejected from the nozzles and controllably directed toward a recording medium (e.g., paper) to print images thereon. Droplet formation can be controlled by, for example, piezoelectric transducers or resistive heating elements as is well known in the art. See, for example, U.S. Pat. Nos. 4,463,359 to Ayata et al; 4,789,425 to Drake et al; 4,638,328 to Drake et al; and 4,601,777 to Hawkins et al, the disclosures of which are incorporated herein by reference.
The nozzles are formed, for example, by etching a plurality of channels in one surface of a first silicon wafer, which is then adhesively bonded to another silicon wafer. The bonded silicon wafers are then diced along a line perpendicular to and intersecting the channels to form a planar surface (or front face) of the printhead, which contains an extended linear array of nozzles (corresponding in number to the number of channels formed in the first wafer). See, for example, U.S. Pat. Nos. 4,878,992 to Campanelli; 4,851,371 to Fisher et al; 4,829,324 to Drake et al; Re. 32,572 to Hawkins et al; and 4,774,530 to Hawkins, the disclosures of which are incorporated herein by reference.
In order to eject droplets consistently (i.e., having a consistent size and ejection direction), the planar surface of the printhead which contains the nozzles (and, particularly, the portion of that planar surface where the nozzles are located) must be maintained smooth and scratch-free. Any scratches on the front face of the printhead in the vicinity of a nozzle can interfere with the formation of an ink meniscus at that nozzle, causing drop misdirection. Additionally, the nozzle containing surface of the printhead is frequently treated with a coating which is non-wettable by the ink. The non-wettable coating prevents ink from adhering to the planar, nozzle-containing surface of the printhead, which adhered ink can also interfere with the ejection of new droplets from the nozzles.
The processes which make these printheads result in nozzles having sharp edges. These sharp edges assist in the meniscus formation process, but also increase the probability of contamination building-up in the nozzles because these sharp edges tend to shear small pieces from wiping blades (which are used to remove excess ink from the front face, particularly after priming), which pieces then collect in the nozzles.
Air can become ingested into the channels which supply ink to the nozzles during operation of the printhead. This air disrupts the operation of those nozzles and is typically removed by priming. Priming can also be used to remove dirt from the printhead nozzles. Dirt accumulates due to the close proximity of the printhead to the paper (which releases dust and particles), as well as due to the presence of airborne dust and particles. Additionally, as discussed above, when wiping blades are used to wipe residual droplets from the planar nozzle-containing surface of the printhead, the sharp edges of the nozzles slice small pieces from the wiping blades, which further clog the nozzles.
A number of procedures are known for priming printheads with fresh ink. Pressure can be applied to the ink supply to force ink out through the nozzles. Alternatively, suction can be applied to all of the nozzles in the printhead to draw ink simultaneously through all the channels. As another alternative, suction can be applied to a lesser number of nozzles (i.e., not all of the nozzles) at a time through one or more tubes or small diameter hoses.
Of these methods, the use of a single tube or hose is preferable because: a) suction is better than pressure for removing air inside the ink jet reservoirs; and b) application of suction to all of the nozzles in the printhead, while being effective for drawing a vacuum through all of the nozzles and removing air, does not function well at removing dirt from the nozzles. The use of a single small diameter tube to apply vacuum to a lesser number of nozzles at one time concentrates the vacuum in that lesser number of nozzles, allowing greater flow through the channels than would occur when applying suction to all of the nozzles at one time. Additionally, the present inventors have found that positioning a small diameter tube closely adjacent to, yet spaced away from, a nozzle-containing front face of the printhead removes more dirt by drawing in air located adjacent to the front face, as well as ink located in the channels. Accordingly, as compared to a single small diameter tube, a cleaning device which applies vacuum to all nozzles at the same time does not apply a force which is sufficient to adequately remove dirt from the nozzles. Additionally, much of the vacuum is lost through the large sealing surface of priming members which suction all nozzles at once. Furthermore, priming stations which suction all nozzles at once tend to leave ink on the front face of the printheads, which ink must be removed, for example, by wiping blades. As discussed above, minute pieces of blade material are cut from the wiping blades by the nozzles, contributing to recontamination of the nozzles.
U.S. Pat. No. 4,947,191 to Nozawa et al discloses an ink jet recording apparatus having an ink jet head provided with plural discharge openings and a partial capping member for covering a part of the plural discharge openings and applying suction only to the covered part of the plural discharge openings. The partial capping member is provided on a belt which is moved across the nozzles of the printhead to selectively locate the partial capping member adjacent to a small number of nozzles. The capping member of Nozawa et al contacts the printhead face along the array of nozzles and is moved along the array of nozzles. The capping member of Nozawa et al could scratch the printhead surface, as well as remove any coating material therefrom. The present invention differs from Nozawa et al at least in that the present invention provides a priming station which does not contact the areas of the printhead containing the nozzles and/or does not slide a priming member along the nozzle-containing surface of the printhead.
U.S. Pat. No. 4,567,494 to Taylor discloses a nozzle cleaning, priming, and capping apparatus for thermal ink jet printers. The cleaning, priming and capping apparatus includes an elastomeric suction cup which engages the printhead during a cleaning, priming or capping operation. The present invention differs from Taylor at least in that the priming station of the present invention does not contact and/or slide along the nozzle-containing surface of the printhead, and also does not prime all nozzles at one time.
U.S. Pat. No. 4,833,491 to Rezanka discloses multiple priming units for contacting multiple printheads on a multi-color carriage-type printer. Each purging unit includes tubing which is placed in air-tight position over the nozzles for application of vacuum thereto. The present invention differs from Rezanka at least in that the priming station of the present invention applies a vacuum to less than all of the nozzles in an array at one time.
U.S. Pat. No. 5,051,761 to Almon Fisher et al, the disclosure of which is incorporated herein by reference, discloses a sliding priming station for priming a small number of nozzles at one time in a pagewidth ink jet printhead. This priming station is located inside a belt or drum (platen) and accesses the printhead by moving through an aperture in the belt or drum. This patent does not disclose an arrangement where a sliding priming station does not contact and/or slide along the nozzle-containing portion of a printhead.